New, independent analyses conducted in Europe and the United States refute a theory that an oral polio vaccine used decades ago in Africa provided the transmission route for HIV or a related virus from chimpanzees to humans.

In his 1999 book, The River, author Edward Hooper contended that the vaccine was made with chimpanzee cells infected with simian immunodeficiency virus (SIV), the virus that experts generally believe gave rise to HIV. Researchers who developed the vaccine at Philadelphia's Wistar Institute have maintained that they did not use any chimpanzee cells in its preparation. The vaccine was administered in clinical trials in the former Belgian Congo during the late 1950s.